Provide macros corresponding to the Unicode general categories

Right now it seems very difficult to write a rule e.g. for words starting with an uppercase letter.

The issue names no files, tests, or entry points. Start by locating Alex's macro and Unicode character-category handling, then trace how lexer rules are represented and tested. Done means the relevant Unicode general-category macros support rules such as words beginning with uppercase letters, with regression coverage.

Written by the indexing model from the issue text.